CyberSecBulletin
CVE-2026-45866NVD status: Analyzed

Linux: Use After Free

Published Updated By the CyberSecBulletin desk

CVE-2026-45866 is a high-severity use after free vulnerability in Linux, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists versions 5e266ba8d330d3b8e5bc198f238cd8901826cfa1, d3c75db4e0460641dbcd274b40867e252d801da1, 4e63d6f68544ae5269ac9735ae5b69b59b5b8725 as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.16% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update Linux to 5e266ba8d330d3b8e5bc198f238cd8901826cfa1 or d3c75db4e0460641dbcd274b40867e252d801da1 or 4e63d6f68544ae5269ac9735ae5b69b59b5b8725 or 331e2b7051635780edea248dd08ae2026c126f4a, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 5.10.252 or 5.15.202 or 6.1.165 or 6.6.128, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinux56e0ef527b184b3de2d7f88c6190812b2b2ac6bf up to, but not including, 5e266ba8d330d3b8e5bc198f238cd8901826cfa1; 56e0ef527b184b3de2d7f88c6190812b2b2ac6bf up to, but not including, d3c75db4e0460641dbcd274b40867e252d801da1; 56e0ef527b184b3de2d7f88c6190812b2b2ac6bf up to, but not including, 4e63d6f68544ae5269ac9735ae5b69b59b5b8725; 56e0ef527b184b3de2d7f88c6190812b2b2ac6bf up to, but not including, 331e2b7051635780edea248dd08ae2026c126f4a; 56e0ef527b184b3de2d7f88c6190812b2b2ac6bf up to, but not including, 52731ef4438155cea782fac74e547a327ab9e7c5; 56e0ef527b184b3de2d7f88c6190812b2b2ac6bf up to, but not including, c8c197aaa56b25a2d54f3aa07e27e228d6c08546; 56e0ef527b184b3de2d7f88c6190812b2b2ac6bf up to, but not including, 40962f2bf8cdba63af23aec95ad3f49b689e58e2; 56e0ef527b184b3de2d7f88c6190812b2b2ac6bf up to, but not including, 308e7e4d0a846359685f40aade023aee7b27284c; and 1 more ranges5e266ba8d330d3b8e5bc198f238cd8901826cfa1, d3c75db4e0460641dbcd274b40867e252d801da1, 4e63d6f68544ae5269ac9735ae5b69b59b5b8725, 331e2b7051635780edea248dd08ae2026c126f4a, 52731ef4438155cea782fac74e547a327ab9e7c5, c8c197aaa56b25a2d54f3aa07e27e228d6c08546
LinuxLinux Kernel3.11 up to, but not including, 5.10.252; 5.11 up to, but not including, 5.15.202; 5.16 up to, but not including, 6.1.165; 6.2 up to, but not including, 6.6.128; 6.7 up to, but not including, 6.12.75; 6.13 up to, but not including, 6.18.14; 6.19 up to, but not including, 6.19.45.10.252, 5.15.202, 6.1.165, 6.6.128, 6.12.75, 6.18.14

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
LocalThe attacker needs local access or must trick a user into running something.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
LowA basic user account is enough.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.

Official description

In the Linux kernel, the following vulnerability has been resolved: serial: caif: fix use-after-free in caif_serial ldisc_close() There is a use-after-free bug in caif_serial where handle_tx() may access ser->tty after the tty has been freed. The race condition occurs between ldisc_close() and packet transmission: CPU 0 (close) CPU 1 (xmit) ------------- ------------ ldisc_close() tty_kref_put(ser->tty) [tty may be freed here] <-- race window --> caif_xmit() handle_tx() tty = ser->tty // dangling ptr tty->ops->write() // UAF! schedule_work() ser_release() unregister_netdevice() The root cause is that tty_kref_put() is called in ldisc_close() while the network device is still active and can receive packets. Since ser and tty have a 1:1 binding relationship with consistent lifecycles (ser is allocated in ldisc_open and freed in ser_release via unregister_netdevice, and each ser binds exactly one tty), we can safely defer the tty reference release to ser_release() where the network device is unregistered. Fix this by moving tty_kref_put() from ldisc_close() to ser_release(), after unregister_netdevice(). This ensures the tty reference is held as long as the network device exists, preventing the UAF. Note: We save ser->tty before unregister_netdevice() because ser is embedded in netdev's private data and will be freed along with netdev (needs_free_netdev = true). How to reproduce: Add mdelay(500) at the beginning of ldisc_close() to widen the race window, then run the reproducer program [1]. Note: There is a separate deadloop issue in handle_tx() when using PORT_UNKNOWN serial ports (e.g., /dev/ttyS3 in QEMU without proper serial backend). This deadloop exists even without this patch, and is likely caused by inconsistency between uart_write_room() and uart_write() in serial core. It has been addressed in a separate patch [2]. KASAN report: ================================================================== BUG: KASAN: slab-use-after-free in handle_tx+0x5d1/0x620 Read of size 1 at addr ffff8881131e1490 by task caif_uaf_trigge/9929 Call Trace: <TASK> dump_stack_lvl+0x10e/0x1f0 print_report+0xd0/0x630 kasan_report+0xe4/0x120 handle_tx+0x5d1/0x620 dev_hard_start_xmit+0x9d/0x6c0 __dev_queue_xmit+0x6e2/0x4410 packet_xmit+0x243/0x360 packet_sendmsg+0x26cf/0x5500 __sys_sendto+0x4a3/0x520 __x64_sys_sendto+0xe0/0x1c0 do_syscall_64+0xc9/0xf80 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f615df2c0d7 Allocated by task 9930: Freed by task 64: Last potentially related work creation: The buggy address belongs to the object at ffff8881131e1000 which belongs to the cache kmalloc-cg-2k of size 2048 The buggy address is located 1168 bytes inside of freed 2048-byte region [ffff8881131e1000, ffff8881131e1800) The buggy address belongs to the physical page: page_owner tracks the page as allocated page last free pid 9778 tgid 9778 stack trace: Memory state around the buggy address: ffff8881131e1380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8881131e1400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >ffff8881131e1480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff8881131e1500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8881131e1580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ================================================================== [1]: https://gist.github.com/mrpre/f683f244544f7b11e7fa87df9e6c2eeb [2]: https://lore.kernel.org/linux-serial/[email protected]/T/#u

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Use After Free

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.

How developers prevent this class of flaw

  • Choose a language that provides automatic memory management.
  • When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.

More Use After Free vulnerabilities (CWE-416)

Timeline

  1. CVE record published.
  2. Record last changed materially (score, affected products, status or references).

References

Recent Use After Free vulnerabilities

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